This invention relates to cell texture, and, more particularly, to microtexture for providing adequate detail when the distance between an observer and a feature in an image to be displayed is less than a predetermined threshold.
In computer image generation systems, cell texture may be used to provide visual detail for surfaces (often represented by faces or polygons) of objects or features to be displayed. However, as the distance between an observer or viewpoint and the object or feature decreases, the size of the image of a cell increases, so that when the image of a single cell is rendered by more than one pixel of a display means, the texture pattern loses some definition and tends to become fuzzy. (A cell is the smallest unit of characteristic definition that is accessible by the system and a pixel is a picture element of the display means). Reduction of texture definition may result in a loss of motion cues from the display that are necessary for adequate and realistic training exercises, such as airplane pilot training.
In one type of computer image generation system, the distance from an observer into a scene to be displayed is divided into a plurality of predetermined range intervals. Each range interval corresponds to a respective level of detail (LOD). The LOD's are arranged so that the LOD closest the observer, or maximum LOD for the system, (hereinafter designated "LOD(0)") contains the most detail and therefore the largest number and smallest sized cell for a predetermined area, with each succeeding LOD (i.e. receding from the view-point) containing a respective decreasing amount of detail with correspondingly smaller number and larger sized cell for the same area. For example, since typically a binary system of data storage and manipulation is used, it is convenient to have adjacent LOD's vary by a factor of four (i.e. a factor of two in each of logically orthogonal X and Y addresses of data storage areas) in amount of detail and cell size.
No matter where the boundary closest to the viewpoint of the maximum LOD is established, there may be occasion to display portions of the scene which are closer to the viewpoint than the nearest boundary of LOD(0). Although additional specific detail could be stored for LOD's closer to the viewpoint than LOD(0) (such LOD's are referred to hereinafter as having a negative argument, e.g. LOD(-1), LOD(-2), etc.), it would generally be infeasible, both economically and practically, to do so, since the additional memory required for an extra LOD would be four times the memory requirement of the next less detailed LOD. For example, six additional LOD's having more specific detail than LOD(0) would require over 8,000 times more memory than a system having a most detailed LOD of LOD(0). The term "specific detail" refers to detail which defines a predetermined feature of an object, such as contour, whereas the term "non-specific detail" refers to a feature of an object, such as texture, that may be hinted or suggested. Of course, there may be occasions when it is desirable to represent a feature, such as texture, by both specific and non-specific detail, dependent on the distance from a viewpoint to the object.
Accordingly, it is an object of the present invention to provide apparatus and method for supplying texture detail to close-in surfaces without unduly increasing memory size requirements.
Another object is to provide apparatus for supplying texture detail to close-in surfaces wherein the apparatus may be readily retrofitted into an existing image generation system.